The coding standard followed in this code base is similar in most ways to the style followed by the Linux kernel. Naturally there are exceptions. Most notably is the indentation (more on this later). Above all else we ask that when modifying the code that you follow the most important rule: check the surrounding code and imitate its style [1].
Code should hold as close to the C99 standard as possible with the exception that GCC specific extensions are generally accepted. The code must compile without warnings for the primary target compiler when all warnings are enabled. If a warning is unavoidable, the offending line must be documented with an explanation of why said code can not be modified to appease the compiler [2].
It is worth noting however that this code base has yet to run into a compiler warning that wasn't the authors fault. It is likely that if you do find yourself disabling -Werror you're probably doing something wrong.
There are two acceptable commenting styles: block, line. Block comments are used to document a largeish block of code, typically a function. Sometimes block comments are useful with a function to document a loop or a particularly tricky part of an algorithm. Line comments are typically a single sentence on a single line. They provide some brief explanation of a line or two of code.
NOTE: Comments are most useful to convey the purpose, parameters and results from functions and objects in a system. Excessive use of comments within a function is indicative of two things: over documentation and code that needs to be refactored. To combat the first case let's say that it's safe to assume that your code will be read by competent C programmers. The second case can be tricky and there's no rule of thumb. Follow your instincts and keep in mind that excessive line comments are a sort of "code smell" that may mean your code would benefit from some restructuring.
/* * This block comment could apply to some function and describe its inner * workings. Notice these sentences have traditional capitalization and * punctuation... that's because it has to be read in a way completely * unlike the Post-It style content of next-line and line comments. */
// This is *not* an acceptable block comment. // Don't do this. // Please.
/* This is a line comment */
All indentation must be spaces, not tabs. Lines are indented in multiples of 4 spaces. Each line of code and documentation will end with a non-whitespace character. There must not be any whitespace between the last line of code or documentation in a file and the end of the file.
Names should clearly convey the purpose of whatever is being named. While the data type of a variable conveys some information, this alone is insufficient. Multiple word names are descriptive and most easily read if words are separated with the underscore character, "_".
Variable and function names must be lowercase. Words in each name must be separated by an underscore character: "_". Macros and constants (anything declared with #define) must be in all-caps, again with words separated by underscores.
Objects created using the GObject system follow the GObject naming convention with individual words in object names as upper case characters.
Exceptions to these rules are made for compliance with the TCG specifications. All function names, parameters, and other data types must be implemented faithfully to the specification and so may violate the naming conventions defined here.
unsigned int table_index = find_index(jacket_table, “color”, COLOR_RED);
int last_item = 0; while (!last_item) { /* ... */ }
int char_found = is_alpha (c);
Single letter variable names should be avoided. Exceptions are:
Abbreviated words in variable names should be avoided. Exceptions are:
Function names should follow the naming conventions of variables and clearly describe not only what the function does, but also the nature of what it returns (if anything). Functions that return boolean integers should be named to reflect the true condition even if they are created to detect false conditions. Functions should never be hidden in conditional statements, with the exception of loops where it makes the code more simple.
bool is_number_prime = is_prime(i);
if (is_number_prime) { /* ... */ }
while (!labeled_correctly(sample[i])) { /* ... */ }
A function that is exported for use in multiple source files should be prefixed with the source file (or object module) name where it is defined. For example, the file list.c may contain the implementation of a dynamic list ADT including an exported method for creating a list instance and an internal (static) method for overflow checking. The first function might be named "list_create", and the second, "is_overflowed".
The use of the static keyword when defining functions is a useful way to scope the visibility of the function to the same translation unit. A negative side effect of this is preventing the testing of the function through the unit testing harness. Generally we accept exposing symbols to get better test coverage.
Typically every header file has the same base filename as an associated source file. Exceptions to this rule are generally limited to modules that will expose a separate set symbols to external consumers. In this case the internal version of the header should be suffixed with '-priv'.
Files names are formatted in the same way as described above with the exception of hyphens "-" separating words.
The body of each header file must be surrounded by an include guard (aka "header guard"). These guards shall be given the same name as the file in which they reside. Their names shall be all caps, with words separated by the underscore character "_".
Header files should never define functions or variables.
Header files should only #include what is necessary to allow a file that includes it to compile. Associated source files will always #include the header of the same name, but should #include files whose resources are used within the source even if they are already included in that header. This provides a complete context for readers of the source file... i.e., they don't have to search through headers to determine where a resource came from.
Files included by all source files must conform to the following format and order. Each entry in the list below defines a contiguous block of include directives separated by a blank line:
install build target. These must be included using the quoted include variant (using " instead of the angle brackets).Headers in each block must listed in alphabetical order.
header: example-module.h
/* * BSD license block */ #ifndef EXAMPLE_MODULE_H #define EXAMPLE_MODULE_H #include <stdint.h> #include <sys/types.h> #include "tss2/tss2_tpm2_types.h" #include "internal-module.h" /* * preprocess or directives and declarations using stuff from included headers */ #endif /* EXAMPLE_MODULE_H */
implementation: example-module.c
/* * BSD license block */ #include <inttypes.h> #include <stdint.h> #include <foo/bar.h> #include "tss2/tss2_tcti.h" #include "tss2/tss2_tpm2_types.h" #include "example-module.h" #include "internal-module.h" /* * Implementation / code using headers listed above. */
Types shall be selected for their use case. Variables should only be of a signed type if something should ever be negative. A common, incorrect use, is to declare loop counters as int instead of unsigned, or to use an int to hold the size of some object.
Always use space characters, 4 spaces per level of indentation.
Conditional statements (such as if, else, while, for, switch, etc) must place the opening brace on the same line after the end of the control flow statement. The closing brace should be placed at the same column position as the beginning of the associated control flow statement on a line by itself.
Function definitions specify the return type on a line, followed by the function name followed by the first parameter. Each additional parameter is listed on a separate line aligned with the line above. The opening brace defning the functions scope must be on the following line at column position 0.
A space must separate a control flow statement or function and the opening parenthesis.
Line length should not exceed 80 characters and should be split on the nearest whitespace or delimiter character. When splitting lines with
if (some_int > 0) { statement1; statement2; }
void some_function (short_t arg_1, longer_name_t arg_2) { statement1; statement2; }
some_long_variable_name = some_long_function_name (lots_of_parameters_1, lots_of_parameters_2);
some_long_variable_name = some_long_function_name (lots_of_parameters_1, lots_of_parameters_2, lots_of_parameters_3);
These formatting conditions are contrary to Kernighan and Ritchie's "one true brace style" [3].